With the improvement of people's living standard, canned food and beverage are increasing, and the demand for the can is also growing.
The can is usually made of aluminum or steel, and composed of a can body and an easy-open end, where the can body is formed mostly by metal draw and iron. An existing can body maker is usually composed of a drawing die, a cup feed station, a can out conveyor, a cup hold down mechanism and a ram drive mechanism. The drawing die is used for drawing and ironing the can body, the cup feed station for transferring a can parison (a pre-drawn cup-shaped part) before it is drawn, the can out conveyor for discharging and outputting the can body after it is drawn, the cup hold down mechanism for tightly compressing the edge of the cup while drawing, and the ram drive mechanism for providing the ram stroke when the can body is drawn.
U.S. Pat. No. 4,173,138 discloses an disclosure patent titled Can Bodymaker Having Improved Ram Support and Drive, which relates to a can body maker, whose ram drive mechanism, as shown in FIGS. 1-3, comprises a crankshaft 14, a primary connecting rod 13, a swing lever 12, a secondary connecting rod 11, a hydrostatic guide rail 9, a slide yoke 10 and a ram 15; the primary connecting rod 13 is rotatably connected at one end with the throw of crankshaft 14, and at the other end with the swing arm of the swing lever 12; the swing lever 12 is rotatably supported at one end, and rotatably connected at the other end with one end of the secondary connecting rod 11, which is rotatably connected at the other end with the slide yoke 10 installed on the hydrostatic guide rail 9; the ram 15 is fixedly connected at one end with the slide yoke 10, and provided at the other with a punch used for drawing the can body. In the working condition, the crankshaft 14 is radially supported by a hydrodynamic journal bearing (not shown in the figure); while the can body is drawn, a motor drives the crankshaft 14 to rotate, the throw of crankshaft 14 drives the primary connecting rod 13 to move, which pushes the swing lever 12 to swing; the swing lever 12 drives the slide yoke 10 to slide along the hydrostatic guide rail 9 through the secondary connecting rod 11, thus driving the punch of the ram 15 to produce a ram stroke. Each time the crankshaft 14 rotates one circle, the punch of the ram 15 produces one ram stroke relative to the drawing die to draw out a can body, the process thus being continuously circulated to draw out the can body.
In the structural design of the can body maker of the above US patent, because only one ram drive mechanism is adopted for the one-way double-action body maker, the inertial force in motion and the reaction force generated by such parts as the swing lever 12, the slide yoke 10 and the ram 15, after the amplification of various transmission mechanisms, are finally entirely exerted on the main bearings supporting the crankshaft 14. Particularly when the crankshaft 14 works at a rotational speed of 400 rpm, these forces form a very big impact load on the main bearing. Therefore, as can be seen from the force analysis, the main bearing supporting the crankshaft 14 in this mechanical structure is the key of force balance and the weakness of the entire mechanism. A rolling bearing is difficult to withstand a greater impact load for a long time, a hydrodynamic journal bearing adopting a high-pressure oil supply system is needed.
For resolving the above problem of supporting the crankshaft in the ram drive mechanism, U.S. Pat. No. 5,546,785 titled Crankshaft Mechanism for Can Body Maker Apparatus provides a solution, i.e. a counterbalance-mass slide yoke is connected at a position contrary to the throw of crankshaft, and used for balancing the load exerted on the bearing by the inertial force of the mechanism itself (see the counterbalance-mass slide yoke 308 in FIG. 3 and the counterbalance-mass slide yoke 230 in FIG. 4 of the U.S. Pat. No. 5,546,785 for details). However, this solution can only balance the inertial force load exerted on the bearing generated by such motion parts as the swing lever 12, the slide yoke 10 and the ram 15 in motion, while the reaction force generated during the can body redrawing and ironing process cannot be balanced by the counterbalance-mass slide yoke. Besides, the addition of the counterbalance-mass block in the ram drive mechanism virtually increases the load of the drive motor, directly causing increase of the power consumption, causing waste of energy.